I've extracted the spider mob of LordofTheTested subgame (viewtopic.php?f=15&t=5578), and i hope it will give you fun ! :)
This mod is for server administrators who aren't programmers, or don't want to do the work themselves done in this mod.

So, it's a mod with just the spider, i've also make smalls modifications :
- updated the spider api.lua (better IA)
- adjusted her HP for a better average (now 15 to 30)
- her jump step (now can jump over 1 block)
- her drops for a better average and add raw_meat sometimes, much culture eats spiders after all (now 50% 1 to 3 string and 25% 1 to 2 meat_raw)
- add blood when hit
- add knock back when hit
- modified spawn, mostly in jungle. Be careful, they spawns in part on "jungle leaves" and "jungle trees" so, sometimes they falls in your head !

Install : Unzip the distribution archive, rename the resultant "minetest-spidemob-v1" folder to just "spidermob", and move it into Minetest's mods directory. At last, Set to true the mod in the "world.mt".

Don't worry about the warning message, it's normal, my SSL certificate isn't signed BUT my Pydio(FTP service used) is over SSL, it's a security protocol...
So, just ignore the warning, download the mod, and install it.

Indeed, you can see "Temporary link", i create a repository in Github when i can...

As you can see, the chance to spawn a spider is relative low with a value of 1/7500.
If you lower this value, like I did it for testing in the extraction guide for this mod here, you will see much more spiders spawning on the nodes you defined. Of course, 60 is good for testing, but maybe a bit too much for a game :) You can also adjust the light values, maybe you want to be safe with placing lightsources (so max light should be lower) or you dont want the spiders to be spawned on mountains (there is also stone at the surface), so you maybe want to lower the max height value (maybe something around -20).

Hey man this mod is too.........SCARY!!!!!!
I nearly died of fright once when I was on this server building my home on a nice little beach bordering a jungle, and all of a sudden....................THAPALMARKXTHTRWERGDSXXTRTYREGDFHG!!!!!
Only luckily I had previously obtained /fly privilege from the server's owner (Username = Admin :D) on account of the trees being excruciatingly tall.
Never new how useful it was going to be.
The owner came to my place and took out the spider, but it still gives me the creepy crawls to even THINK of that.